This section provides background information related to the present disclosure which is not necessarily prior art.
As illustrated in FIGS. 1 and 2, a conventional heat exchanger 10 of the plate fin-type generally include a plurality of parallel tubes 12 having a plurality of perpendicular fins 14. The plurality of perpendicular fins 14 are thermally coupled with a plurality of parallel tubes 12 to serve as an evaporator (heat exchanger 10). Heat absorbing fluid is forced through a capillary tube into the plurality of parallel tubes 12 at a low temperature and pressure. Subsequent evaporation of the fluid removes heat energy from the air passing adjacent the tubes of the evaporator, thus cooling the air. The fins 14 attached to the tubes 12 increase the effective heat absorbing area over which the airflow is directed, thus increasing the cooling efficiency of the evaporator. A small motor driven fan 16 may be utilized to draw air over the heat absorbing area of the evaporator and discharge the cooled air into the interior of the refrigerator.
It should be understood, however, that air flow distribution is affected by both the evaporator design and fan 16 placement. In many cases, a majority of the air flows directly under the fan 16 and less at the ends 18 of the heat exchanger 10, which results in a misdistribution of air flow that reduces heat transfer. This phenomenon is illustrated in FIG. 1.
Moreover, the tubes 12 of evaporator 10 are spaced evenly across the depth of the evaporator 10. However, for manufacturing and design purposes, this is often not the case. Thus, uneven gaps 20 between tubes 12 will disrupt the distribution of airflow, with more air flowing through the larger gaps as shown in FIG. 2. In this case, less air contacts the tubes 12, which decreases the amount of heat transfer.
Further, due to noise concerns, household refrigerators utilize small fans that yield lower airflow rates, with typical Reynolds numbers being in the range of 300 to 1200. These small fans are very sensitive to pressure drop and an increase in pressure drop can further reduce air flow, which degrades the amount of heat transfer. In addition, with this type of airflow, minimal improvement is seen from the traditional fin enhancements such as the use of louvers, rippled fins, and vortex generators. These types of enhancements perform best in configurations having higher Reynolds numbers, which represents the amount of turbulent flow that is used in many applications such as HVAC and commercial refrigeration, and is defined as follows:Re=ρVDh/μ  (1)
where ρ=density of air; V=air velocity; μ=air viscosity; and Dh=hydraulic diameter, defined as Dh=4 Aflow(min)L/Asurf, where Aflow(min)=the minimum cross sectional area the air flows through; L=the flow length of the evaporator; and Asurf=the surface area exposed to airflow.